Thyroid nodularity and chromosome aberrations among women in areas of high background radiation in China.

Thyroid nodularity following continuous low-dose radiation exposure in China was determined in 1,001 women aged 50-65 years who resided in areas of high background radiation (330 mR/yr) their entire lives, and in 1,005 comparison subjects exposed to normal levels of radiation (114 mR/yr). Cumulative doses to the thyroid were estimated to be of the order of 14 cGy and 5 cGy, respectively. Personal interviews and physical examinations were conducted, and measurements were made of serum thyroid hormone levels, urinary iodine concentrations, and chromosome aberrations in circulating lymphocytes. For all nodular disease, the prevalences in the high background and control areas were 9.5% and 9.3%, respectively. For single nodules, the prevalences were 7.4% in the high background area and 6.6% in the control area (prevalence ratio = 1.13; 95% confidence interval = 0.82-1.55). There were no differences found in serum levels of thyroid hormones. Women in the high background region, however, had significantly lower concentrations of urinary iodine and significantly higher frequencies of stable and unstable chromosome aberrations. Increased intake of allium vegetables such as garlic and onions was associated with a decreased risk of nodular disease, which seems consistent with experimental studies suggesting that allium compounds can inhibit tumor growth and proliferation. The prevalence of mild diffuse goiter was higher in the high background radiation region, perhaps related to a low dietary intake of iodine. These data suggest that continuous exposure to low-level radiation throughout life is unlikely to appreciably increase the risk of thyroid cancer. However, such exposure may cause chromosomal damage.

[Epidemiological survey in a high background radiation area in Yangjiang, China].

The results of the health survey in a high background radiation area (HBRA) from 1972 to 1990, in Yangjiang, China, are presented in this paper. Radiological measurements of the environmental and human bodies with different methods revealed that 330 mR/a in HBRA and 114 mR/a in the control area (CA) were the doses that annually an individual exposure to the external environmental gamma radiation and effective doses to whole body are 6.4 mSv in HBRA and 2.4 mSv in CA annually. The carcinogenic and mutagenic factors were surveyed. The Results showed that these factors in the two areas were similar. Up till now, no harmful impact induced by natural radiation, based on the data as: cancer mortality from 1,008,769 person-years in HBRA and 995,070 person-years in CA; hereditary diseases and congenial malformations from 13,425 subjects in HBRA and 13,087 subjects in CA; human chromosome aberrations, and immune function of the inhabitants, was found. In addition, in this paper the authors discussed the results of cancer mortality, of chromosome aberrations and of immune function, and analyzed the possible relationship among them. The carcinogenic risk induced by low dose radiation was also estimated and discussed.